In many applications, including the production of window and door frames, the use of a pultruded fiberglass profile with one or more hollow cavities is desirable based on its favorable strength, thermal and material properties. However, significant manufacturing limitations exist with respect to current processes for pultruding fiber reinforced polymer based profiles, especially when using polyurethane resins. To pultrude a continuous profile with a hollow cavity, the pultrusion toolset requires an elongated mandrel supported only at the beginning stage of the pultrusion process. This presents many technical difficulties and cost disadvantages in comparison to the production of non-hollow profiles. The design, manufacture and set up of a mandrel toolset takes significantly longer, increasing costs by 40%-100% over non-mandrel toolsets. The production output of a mandrel toolset may be 50%-75% less because the line speed must be reduced to account for reduced heat control. In addition, the strain on the process puller may be increased by a factor of 5 to 10 times due to the drag of the mandrel on the part as it cures and shrinks during processing. But most importantly, because the mandrel may only be supported in the first 10 inches of the input end of the toolset, which is normally 90 to 100 inches long, the mandrel is subject to much flexing and movement from the hydraulic pressures exerted 80 to 90 inches downstream. Such flexing and movement of the mandrel destabilizes the process, which adversely affects the consistency of the wall thickness and the overall dimensional stability of the hollow profile. As a result, pultruded hollow profiles commonly have lower part quality and consistency than non-mandrel/non-hollow profiles.
Accordingly, an improved process for producing elongated hollow profiles is needed. In particular, an improved process is needed for manufacturing elongated fiberglass tubes using a continuous pultrusion process.